In the production of formation fluids, including crude oils and other hydrocarbons, the characteristics of the formation can have a substantial effect on the efficiency of production. Recovery of formation fluids is frequently difficult when the subterranean formation is comprised of one or more incompetent or unconsolidated sand layers or zones. Sand layers in the incompetent or unconsolidated sand zone can move or migrate into the well bore during the recovery of formation fluids from that zone. As is well known, the movement of sand into well bore can cause the well to cease production of reservoir fluids. Not only can fluid production be reduced or even stopped altogether if sand particles flow from the well to the surface, serious mechanical problems can result from the passage of abrasive sand particles through pumps and other mechanical devices.
A conventional technique for completing a well in an incompetent formation to substantially prevent entrainment of earth particles into the well involves running one or more strings of casing into the well bore and then running the actual production tubing inside the casing. At the wellsite, the casing is perforated across the productive zones of the reservoir to permit production fluids to enter the well bore. While it is possible to have an open face across the oil- or gas-bearing zone, it is such an arrangement which permits formation sand to be swept in to the well bore. To correct this problem, sand screening is usually employed in the region opposite the casing perforations. Packers may also be used above and below the sand screens to seal off the portion where production fluids flow in to the tubing from the rest of the annulus. The annulus around the screen is conventionally packed with relatively coarse sand or gravel to reduce the amount of formation sand reaching the screen. A work string is used to spot the gravel around the screen, as those skilled in the art readily understand. The gravel can be hydraulically placed in the annular void space by circulating a suspension of the gravel in water or some other liquid through the void space so that the gravel is deposited therein.
Ideally, the gravel so placed should fill the annulus between the sand screen and the casing. Unfortunately, spaces often remain within the annulus which are not filled with gravel. These spaces will eventually become filled with accumulated formation sand, forming sand plugs or bridges. In practice a number of such bridges may occur, particularly in long perforate liners. Sand bridges greatly reduce the effectiveness of the gravel pack by permitting the formation sand to migrate through the sand bridges and into the production flowpath, resulting in the problems previously decribed.
a variety of tools and processes have been developed to minimize the occurrence of voids and sand bridges in the gravel pack. One such conventional process employs a washing tool to wash the perforations in casing and sand control screens. By establishing flow at relatively high pressures, such tools can often open a void in the gravel packing or dislodge a sand bridge. One such tool is commonly referred to as a swab cup straddle-type tool. Such tools create hydraulic turbulence to dislodge sand bridges. Another type of device is disclosed in U.S. Pat. No. 4,711,302, issued to Jennings. This device utilizes a high energy impulse to remove void spaces in an in-casing-type gravel pack. In practice, the device is placed in close proximity to a void space and detonated. Upon detonation, the device generates a level of energy sufficient to create turbulence and agitation of the gravel within the gravel pack. The level of turbulence is said to be sufficient to readjust and consolidate the gravel within the pack.
Althugh these tools and processes which rely solely upon turbulence are often effective in the removal of gravel pack voids and sand bridges, a need still exists for a tool which can deliver a localized force effective to dislodge sand bridges within a gravel packed well completion.